Magnesium alloys



United States Patent MAGNESIUM ALLOYS Rene Lucien, Paris, and Emile Tetart, Louvie-Juzon, France, assignors to Societe dlnventions Aeronautiques ct Mecaniques S. I. A. M., Fribourg, Switzerland, a corporation of Switzerland No Drawing. Application November 10, 1954 Serial No. 468,157

Claims priority, application France August ll, 1954 1 Claim. (Cl. 75--168) In their copending patent application Serial No.

432,576, filed May 26, 1954, the applicants have proposed the use of lanthanum, amongst the rare earth metals commercially usable in alloys of the kind referred to, the lanthanum being in the practically pure state, which implies, in fact, the use of a rare earth metal of which the content in lanthanum is greater than 90%.

The presence of a rare earth metal having this content of lanthanum has very favorable effects upon the alloy from the point of view of micro-porosity, which is thereby ahnost entirely eliminated. However, with such alloys, the mechanical properties are slightly lower than is the case with other rare earth metals, under the usual conditions of preparation, when the zinc content is low.

In the copending application referred to, the applicants proposed the use of rare earth metals having a high content of didymium which has the effect of improving the mechanical properties of the alloy. It has, however, been recognised that the use of didymium in the proportions indicated leaves a certain amount of micro-porosity, although small, in the alloy.

The metallurgist is thus in the following dilemma: either he can proceed to the use of rare earth metals comprising more than 90% of lanthanum with the consequent risk that the mechanical properties become lower as the content of the zinc itself becomes smaller; or he can use rare earth metals having a high content of didymium giving mechanical properties which are less subject to variations in accordance with the zinc content, this advantage being obtained to the detriment of the homogeneity of the structure of the alloy.

The work carried out by the applicants has now established that it is possible to manufacture light alloys of magnesium-Zinc-rare earth metals which have very good mechanical properties and, at the same time, are free from micro-porosity, by a compromise between the two methods referred to above, that is to say by using a mixture of rare earth metals having a high content of lanthanum, which is however less than 90%, and of rare earth metals with a high content of didymium.

Similarly to the above-mentioned copending application, cerium is practically excluded and its content will in no case be greater than of the total weight of the rare earth metals used.

In accordance with the invention, the lanthanum is present in the mixture of rare earth metals to a minimum content of and a maximum content of 75%, the content of neodymium being 10 to 50%, the praseodymium content from 5 to 15% and the samariumcontent from 1 to 17%. These last three elements compensate for the effect of the lanthanum from the point of view of mechanical properties.

A preferred composition of this alloy will remain the same as that indicated in the copending application previously referred'to, namely:

Zinc 5 to 7%. Rare earth metals 0.5 to 2%. Aluminum 0.5% for preference.

Beryllium 0.01%. Silicon Acceptable up to 0.15%. Magnesium The remainder.

The mixture of rare earth metals will have the composition given above, namely:

lanthanum 20 to Neodymium 10 to 50%. Praseodymium 5 to 15%. Samarium 0.5 to 17%. Cerium Less than 10%.

It is however necessary to distinguish between the composition of the rare earth metals employed at the moment of their introduction into the magnesium, and that which obtains in the final alloy.

In practice, the reduction of the salts of rare earth metals by magnesium has an efiiciency which varies in dependence on the particular rare earth metals concerned; thus, by Way of example, a mixture of salts of the rare earth metals having the composition indicated below, will give very satisfactory results:

Percent Neodymium 35 to 50 Praseodymium 6 to 10 Samarium 10 to 12, Lanthanum 30 to 40 Cerium 4 The efiiciency of reduction of the neodymium, praseodymium and cerium is, in general, the highest. That of the lanthanum is a little less and that of the samarium is very low. Finally, the composition obtained actually in the alloy is, by Way of example and not in any sense of limitation, as follows:

Percent Neodymium 40 to 65 Praseodymium 8 to 12 Samarium 0.5 Lanthanum 25 to 35 Cerium 2 to 10 Percent Lanthanum 25-35 Neodymium 40-65 Praseodymium 8-12 Samarium 0.5 Cerium 2-10 and the balance magnesium.

References Cited in the file of this patent UNITED STATES PATENTS 2,549,955 Iessup et al Apr. 24, 1951 FOREIGN PATENTS 115,813 Australia Sept. 17, 1942 1,029,295 France Mar. 4, 1953 OTHER REFERENCES Journal of Metals, November 1951, pages 987-993. Journal of Metals, vol. I, pages 968-983, December 1949. 

